The present disclosure relates generally to metal casting and, more particularly, to improvements in casting through gravity and centrifugal force feed through an ingate system.
In conventional sand casting, a cast part is produced by first creating a mold from a sand mixture and then pouring molten liquid metal into the cavity of the mold through an ingate system having an inlet disposed above the top of the mold so that the liquid metal flows under the force of gravity into the cavity through a passageway or sprue and runner. The mold is then allowed to cool until the casting solidifies, and the casting is then separated from the mold. The sand that is reclaimed for reuse. To allow for overall shrinkage as the part cools, the sand mold cavity is made slightly larger than the finished part.
Conventional sand casting poses several problems. When molten metal is introduced through the gating system, air will sometimes become trapped within recesses of the cavity as the level of molten metal rises. When air becomes trapped in this fashion, the finished casting will solidify with a defect, requiring it to be discarded as waste. Thus, great care is given when designing mold configurations and often special vents are provided in the hard-to-reach places, so that air will not become trapped. To ensure that the entire cavity becomes filled, the mold configuration will typically include an extra reservoir or riser at the inlet that contains extra molten metal. The riser allows the foundry operator to pour more metal than is needed to define the finished part. This extra metal provides a head of pressure that forces extant gasses through the vents and/or permeable surface of the mold and ensures that the entire cavity is fully filled before solidifying takes place.
Of course, as molten metal is poured into this system, it will ultimately solidify in the sprue, runner, ingates, risers and vents as well. Thus, when the finished part is removed, the excess material that has solidified in the sprue, runner, ingates, risers and vents will need to be cut away and discarded as waste. In conventional practice this removal is performed mechanically, using abrading tools, compressors and the like. Thus a significant amount of electrical energy is consumed in the conventional removal process. Thereafter, the waste material will be melted again for reuse, which consumes significant additional energy.
The modern metal casting foundry, like most other manufacturing businesses, faces considerable pressure to reduce costs, reduce waste, and reduce energy consumption. In this regard, it would be desirable to reduce energy consumption my minimizing the amount of metal needed to be melted for the initial pour; and to further eliminate the waste associated with removal and re-melting of waste for reuse. Given the practical limitations of conventional sand casting, it has not been heretofore been possible to produce casting where the quantity of liquid metal poured in to the mold is sufficient to supply the finished part but constitutes very little additional waste.
The present invention significantly improves energy efficiency, reduces waste, and minimizes the need for risers and vents through a process that uses both gravity feed and centrifugal force feed to very accurately control the flow of molten metal into the mold cavity and thereby minimize the amount of metal remaining in the sprue when the metal cools. If a riser is required, it can be of minimal size thereby minimizing waste. By way of example, a conventional sand casting process will yield approximately 65 pounds of finished product for every 100 pounds of metal poured (65% efficient). The illustrated embodiments described herein will yield approximately 85 pounds of finished product for every 100 pounds of metal poured (85% efficient).
The process uses a rotating table or other rotating apparatus to place the incoming molten metal under a controlled, substantially constant centrifugal force by controlling the ramp-up acceleration and/or velocity of the turntable. Because the molten metal is introduced under very controlled conditions, it is possible to fill most mold cavities without creating air pockets that would other necessitate a vent. The controlled influx technique allows the mold cavity to be filled (1) at a rate that does not damage or degrade the sand mold walls, (2) at a rate that ensures the entire cavity is filled before the metal starts to solidify, and (3) in a controlled quantity that leaves very little excess material that will need to be removed as waste. The controlled influx technique advantageously places the hot spot of the cooling metal at the ingate so that any product shrinkage that occurs when the metal finally solidifies, will occur at the ingate and thus in the sprue and/or riser to be removed.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.